1. Field of the Invention
The present invention relates to a magnetic head which performs recording or reproduction of information signals on a magnetic recording medium, a method for producing the same, and a magnetic recording/reproduction apparatus using the same. It relates particularly to a narrow-track magnetic head for high density magnetic recording used in a digital VCR or the like, a method for producing the same, and a magnetic recording/reproduction apparatus using the same.
2. Description of the Related Art
In order to record/reproduce a large amount of information signals such as found in digital VCR, it is necessary to employ high density magnetic recording/reproduction techniques such as the narrow-track technique and the short-wavelength technique. Generally, it is known that for the realization of high density magnetic recording/reproduction, it is better to increase the coercive force of a recording medium or to increase the saturation magnetic flux density (hereinafter, referred to as a "Bs") of a magnetic head.
However, a ferrite material, which has mainly been used in the prior art as a material for a magnetic head, has a Bs of about 0.5 T, which is not sufficiently large. Therefore, when a prior art magnetic head made of the ferrite material is used on a metal tape having a high coercive force of 80 kA/m or more, there occurs magnetic saturation so that a recording and reproduction of information might not be conducted with certainty.
To resolve the situation, magnetic heads have currently been suggested which are made of a new material having a Bs larger than that of the ferrite material, such as a Sendust alloy film (Bs: about 1.0 T) or a Co type amorphous film (Bs: about 0.8 T to about 1.1 T), or other materials having a Bs of about 1.3 T or more, such as a Co type superstructure nitriding alloy film, an Fe type superstructure nitride film or an Fe type nitride film. Among these, research has been vigorously conducted particularly on a composite magnetic head, or so-called MIG head, in which the main core is made of ferrite and a magnetic thin film is disposed on the surface of the main core at least in the vicinity of the front gap.
FIG. 13 is a perspective view illustrating an example of a configuration of a prior art MIG head.
In the prior art MIG head 500 shown in FIG. 13, a pair of convex or bevelled magnetic cores 502 and 503 are disposed opposite to each other with a magnetic gap 501 being therebetween. The magnetic core 502 includes a convex or bevelled core body 504 (hereinafter, simply referred to as the "core body 504") made of ferrite and a magnetic film 506 which is formed on the surface of the core body 504 and has a high saturation magnetic flux density. Similarly, the magnetic core 503 includes a convex or bevelled core body 505 (hereinafter, simply referred to as the "core body 505") made of ferrite and a magnetic film 507 which is formed on the surface of the core body 505 and has a high saturation magnetic flux density. The magnetic films 506 and 507 are formed so as to cover the projection end faces of the core bodies 504 and 505, respectively, facing the magnetic gap 501, and also completely cover both of the side faces therefrom. The magnetic gap 501 is provided with a nonmagnetic film (referred to as "gap member") not shown in FIG. 13. The magnetic cores 502 and 503 are butted to each other with the magnetic gap 501 including the gap member inserted therebetween. Furthermore, the magnetic cores 502 and 503 butted as such are coupled to each other with a pair of glass blocks 508 and 509 which are disposed at both sides of their butting ends. A winding window 510 for coils to pass is provided at the middle of the side faces of the MIG head 500.
In view of the narrow-track technique, the MIG head 500 described above may not be formed with sufficient accuracy with respect to a track width due to a production error such as butting accuracy of the two magnetic cores 502 and 503, or due to the influence of a roundness at the track edge of the magnetic films 506 and 507. Moreover, since the track width cannot be determined unambiguously, sufficient accuracy may not be obtained during the adjustment steps for the track height during assembly. Consequently, a decrease in the yield may result in the production of the MIG head 500.
In order to solve these problems, the applicant of the present application has suggested an MIG head as disclosed in Japanese Laid-Open Patent Publication No. 7-220218, which corresponds to pending U.S. patent application Ser. No. 08/313,594 filed on Sep. 29, 1994. In FIG. 14, a configuration of the top face of the MIG head 600, i.e., the sliding surface for a magnetic tape, is schematically illustrated.
A fundamental configuration of the MIG head 600 is similar to that of the MIG head 500 described before. A pair of convex or bevelled magnetic cores 602 and 603 are disposed opposite to each other with a magnetic gap 601 being therebetween. The magnetic core 602 includes a convex or bevelled core body 604 (hereinafter, simply referred to as the "core body 604") made of ferrite and a magnetic film 606 which is formed on the surface of the core body 604 and has a high saturation magnetic flux density. Similarly, the magnetic core 603 includes a convex or bevelled core body 605 (hereinafter, simply referred to as the "core body 605") made of ferrite and a magnetic film 607 which is formed on the surface of the core body 605 and has a high saturation magnetic flux density. The magnetic films 606 and 607 are formed so as to cover the projection end faces of the core bodies 604 and 605, respectively, facing the magnetic gap 601, and also completely cover both of the side faces therefrom. The magnetic gap 601 is provided with a nonmagnetic film as a gap member. The magnetic cores 602 and 603 are butted to each other with the magnetic gap 601 including the gap member inserted therebetween. Furthermore, the magnetic cores 602 and 603 butted as such are coupled to each other with a pair of glass blocks 608 and 609 which are disposed at both sides of their butting ends.
The magnetic tape sliding face of the MIG head 600 is provided with notches 613a and 614a over both of the magnetic cores 602 and 603 in addition to a convexly processed part 639 which regulates the track width. By having these notches 613a and 614a, a track misalignment associated with the butting accuracy of the magnetic cores 602 and 603 within the magnetic head 600 is eliminated, and degradation of accuracy due to a roundness of the track edge, or so-called fringe, is also reduced considerably.
However, since a number of processes are also conducted after processing steps for the notches 613a and 614a in the production of the MIG head 600, there may result a track misalignment between the magnetic cores 602 and 603 on a microscopic level, and it may be the case that an initial track width cannot be maintained with sufficient accuracy.
Furthermore, the side faces of the convexly processed or bevelled part 639 of the magnetic cores 602 and 603 are provided with an antireaction film 640 made of a material such as SiO.sub.2, ZrO.sub.2, Ta.sub.2 O.sub.5, glass, Cr, or a composite thereof, at the interfaces between the glass blocks 608 and 609 and the magnetic films 606 and 607. Thus, a chemical reaction between the magnetic cores 602 and 603 (more precisely the magnetic films 606 and 607) and the glass blocks 608 and 609, respectively, is inhibited. However, the interfaces between the magnetic films 606 and 607 and the glass blocks 608 and 609 at the notches 613a and 614a are not provided with such antireaction films 640. Consequently, the chemical reaction may occur therebetween and, as a result, problems such as a blur at the track edge may occur.
Due to problems described above, even with the MIG head 600 illustrated in FIG. 14, problems associated with the accuracy of the track width still remain.
On the other hand, improvement of the accuracy of the track width has been tried in several prior art techniques so far.
For example, U.S. Pat. No. 4,110,902 discloses a method for regulating a track width by a wire from the top face of the sliding face. This is to process the entire sliding face for a fixed track width. However, a problem concerning wear resistivity due to contact with a running magnetic medium may result, and there is a possibility of significant deterioration of magnetic characteristics.
U.S. Pat. No. 3,668,775 discloses a magnetic head which is configured such that a dimension of the entire core matches the track width. However, even with this configuration, there is still a possibility of significant deterioration of magnetic characteristics. Moreover, strength of the magnetic head may deteriorate.
Furthermore, U.S. Pat. No. 5,298,113 discloses a production method for a magnetic head in which the vicinity of a track is processed with a turning tool. In this method, however, there is a possibility that an edge of the magnetic gap, which is a primary part of the magnetic head for conducting magnetic recording/reproduction, is damaged. An occurrence of such damage leads to a deterioration of magnetic characteristics and is not preferable in view of operational characteristics of the magnetic head. Moreover, in view of machining accuracy, it is difficult to process with an accuracy of about 1 .mu.m or less. Particularly, there is a difficulty in keeping constant machining accuracy in the depth direction of the magnetic gap.
Furthermore, in the disclosed machining method using the turning tool, the turning tool must be pressed against the magnetic core to process it into a predetermined shape during actual implementation of the method. As a result, materials in a bar shape cannot be processed, posing a problem associated with the realization of mass production. In addition, a deterioration of magnetic characteristics may occur due to a process-induced denatured layer on the processed surface, posing a problem that a predetermined effective track width cannot be maintained with accuracy.
As a result of the recent improvement of a recording density in magnetic recording, it is becoming a requirement that, for a magnetic head, a track width of about 10 .mu.m or less be obtained with an accuracy of about .+-.0.5 .mu.m or less. However, as has been described above, it is almost impossible with the prior art technique to meet the requirements described above without a deterioration of magnetic characteristics.